Preparation:
Add olive oil to a large deep sauté pan and bring to a medium heat, add chopped yellow onion and sauté for 2-3 minutes, allowing the onion to soften a bit, add the green onion and cod pieces. Season with salt & pepper, cook for 3-4 minutes and add the white wine. Follow with the lettuce leaves, chopped dill and fish stock. Cover and cook for about 20 minutes. Shake the skillet to distribute the ingredients as the fish is delicate and it is best not to use a utensil to stir. While the fish is cooking, the avgolemono (egg-lemon) sauce should be made.

Sauce
Place 3 egg yolks into small bowl with the lemon juice and beat well with a whisk for 3-4 minutes. Add two ladle spoons of stock from the fish and whisk well.
Pour the sauce over the fish, shake the pan well and cook for 2-3 minutes.